Gravity controlled mine firing mechanism



June 30, 1959 R. H. PARK GRAVITY CONTROLLED MINE FIRING MECHANISM 7 Sheets-Sheet 1 Filed Dec. 8, 1941 INVENTOR R- H- PARK ATTORNEY June 30, 1959 R. H. PARK 2,892,402

GRAVITY CONTROLLED MINE FIRING MECHANISM I Filed Dec. 8. 1941 7 Sheets-Sheet 2 INVENTOR R. H PARK BY A I;,ORNEY Jun 30,1959 v 'R PAR'K T 2,892,402

GRAVITY CONTROLLED MINE FIRING MECHANISM INVENTOR ATTORNEY June 30, 1959 R. H. PARK 2,392,402 I GRAVITY CONTROLLED MINE FIRING MECHANISM Filed Dec. 8, 1941 i 7 Sh eets-SheetA INVENTOR R, H, PARK ATTORNEY June 30, 1959 Filed Dec. 8, 1941 R. H. PARK GRAVITY CONTROLLED MINE FIRING MECHANISM 7 Sheets-Sheet 5 INVENTOR R. H. PARK BY ATTORNEY June 30, 1959 R. H. PARK 2,892,402

' GRAVITY CONTROLLED MINE FIRING MECHANISM Filed Dec. 8, 1941 7 Sheets-Sheet 6 I78 we I74 |3l A log;

I i]; a "III INVENTOR :32 I R. H. PARK 203 l 202 BY ATTORNEY June 30, 1959 R. H. PARK ,GRAVITY CONTROLLED-MINE FIRING MECHANISM Filed Dec. 8, 1941 7 Sheets-Sheet? INVENTOR R. H. PARK ATTORNEY PEN GRAVITY CONTROLLED MINE FIRING MECHANISM Robert H. Park, Pluckemin, NJ. 7 Application December 8, 1941, Serial No. 422,038

28 Claims. (Cl. 1(l2-16) (Grantedunder Title 35, US. Code (1952), sec. 266) This invention relates to improvements in firing mecha-- nism for submarine mines and the like wherein anomalies in the attraction of gravity produced by the movement of a foreign ponderous mass within the vicinity of the mechanism are employed to actuate a movable element and thereby set into operation certain control devices to cause the mine to explode. More specifically, the invention provides a gravitationally responsivefiring or control mechanism in which a relatively small mass is continually maintained in va predetermined position of balance regardless of small gravitational changes such, for example, as those produced by the movements of small craft within the vicinity of the mechanism or by the action of tides in the body of water within which the mine is launched, and in which certain electro-responsive devices are caused to operate in a predetermined sequential order in response to more rapid changes in the gravitational force acting on the device thereby to establish a circuit from a source of electric current to an electro-responsive detonating device to operate the detonating device and explode the mine upon the approach.

of. a ponderous mass such, for example, as a vessel within the vicinity of the device. I

The devices heretofore proposed. for controlling the detonation of a submarine mine upon the approach of a vessel usually employdetecting means responsive to changes in the earths magneticfield for-causing the mine to explode as the vessel moves into the vicinity of. the mine and the element employed for such detection usually comprises a magnetized needle or bar pivoted about an axis, or an induction coil adapted to respond to changes in the magnetic field surrounding the mine due to a magneticdisturbance caused by the approaching vessel. Such mines have proved to be not altogether effective in operation by reason of certain preventative measures which have been employed for rendering the vessel sufiiciently non-magnetic in character as to prevent the operation of the mine firing control mechanism whenthe vessel moves within the vicinityof the mine. Furthermore, such devices are obviously unatfected by the movements of wooden ships within the control area of the mine.

The present invention provides a device for controlling the detonation of a mine which is reliable in operation, inexpensive to manufacture, and which is adapted to perform satisfactorily all the functions, and which possesses none of the disadvantages of the prior devices.

As is well known, every particle of matter within the physical universe attracts every other particle of matter with a force proportional to the product of the masses and inversely proportional to the square of the distance between the masses. It will be understood that the gravitational force acting on a particular mass is the resultant of the gravitational forces set up by all of the 2,892,402 Patented-June '30, 19 59 2 disposed somewhat adjacent a particular mass produce greater gravitational effects upon the particular mass than a more distant mass of like weight. The movement of a ponderous mass, such as a vessel, within the vicinity of particular control mass causes relatively rapid changes to be effected in the terrestrial gravitational force acting on the control mass thereby to actuate the control mass in such a manner as to cause a firing circuit to be closed from a source of electrical energy to an electro-responsive detonating device thereby to explode the mine. v

- It is well known that the position of constant gravitational force varies in accordance with the disposition of nearby masses and, therefore, an equipotential sur face is defined' herein as 'a surfacein which the gravitational force is the same throughout the surface, and may be expressed generally by the equation:

going equation, V is a single valued function of xonz, it cannot be two values at the same point and therefore no two surfaces of the family intersect each other.

In the vicinity of an attracting mass V(x,y z) does not define a plane surface and for this reason the curvature of the equipotential surface has'a value other than zero.

The space rate of change of gravitational force in any direction is defined herein as thecomponent of the gradient in that direction; a c

The device of the present invention comprises a gravimeter such, forexample, as the 'Wright gravirneter described in the publication, Geophysical Exploration by C. A. 'Heiland on' page thereof, published by Prentice-Hall, Inc. in 1940,-'or a device for detecting disturbances of the terrestrial gravitational field in which a small boom having a weight and mirror secured thereto is adjusted to a predetermined horizontal position by applying a suitable degree of torsion to a tapering helical by relatively slow variations in the intensity of the gravi-V tational field are compensated for by operating the motor selectively in either direction under control of a photronic cell and an electro-responsive device connected thereto, An arrangement is thus'provided in which relatively slow changes in the gravitational field due to the rise and fall of the tide of the body of water within which the device is disposed arecontinually balanced by variations in the torsional force applied to a resilient spring member by the motor thereby to prevent the detonation of the mine as a result of these slow gravitational changes.

When a ponderous mass such as a vessel approaches within the vicinity of the device, the relatively rapid gravitational change produced by the vessel causes the suspended weight to be actuated from an adjusted position more quickly than the rate of compensation applied by the motor and thus the weight and mirror are moved through an angle of deviation from the adjusted position of the weight greater than the angle of deviation caused by variations in gravitational effects due to tides. When this oc:

with an arrangement for rigidly supporting the ,weight and boom during the launching of the mine and means effective for releasing the weight and boom for operation within a predetermined time after the mine has been launched. The mine is also provided with means for preventing the premature detonation of the mine in response to a disturbance or violent shock received such, for example, as the result of countermining operations.

One of the objects of the present invention resides in the provision of 'a new and improved gravitational influence firing mechanism of simple and rugged construction which will be economical to manufacture and possess the desired qualities of reliability and efliciency in use and operation.

Another object is to provide a new and improved gravitational response device, which, when used as a trigger mechanism of a mine, is adapted to withstand the rough handling of transportation and planting without injuring or changing in any way the adjustment and gravitational or mechanical balance of any of its component parts.

Another object is a provision of a mine firing mechanism having new and improved means for compensating for the gravitational effects of tides of the body of water within which the mine is launched.

Another object of the invention is the provision of a gravitational device responsive to changes in the disposition or movement of a ponderous mass Within the vicinity of the device;

Another object is to provide a novel mine firing mechanism in which the detonation of the mine is controlled by variations in the gravitational field adjacent thereto.

Further other objects, advantages, and improvements will be apparent from the following description taken in connection with the accompanying drawings, of which:

Fig. 1 is a view partially in section and partially broken away of a submarine mine employing the device of the present invention;

Fig. 2. is a view'of the firing control mechanism of Fig. 1 with the cover removed;

Fig. 3 is a view taken substantially along the line 33 of Fig. 2 with the cover in position;

Fig. 4 is a view taken substantially along the line 44 of- Fig. 2 with the cover in position;

Fig. 5 is a view partially broken away taken substantially along the line 55 of Fig. 2;

Fig. 6 is a view somewhat enlarged illustrating the weight clamping and release mechanism of Fig. 4;

Fig. 7 is a plan view, partially in section of the device of Fig. 6;

Fig. 8 is a view somewhat enlarged, partially in section and partially broken away of a pendulum suitable for use with the present invention, and

Fig. 9 illustrates diagrammatically the electrical circuit arrangement of the entire system.

Referring now to the drawings on which like numerals of reference are employed to designate like parts throughout the several views, and more particularly to Fig. 1 thereof on which is shown a submarine mine adapted to be laid on the bed of a body of water comprising a casing 11 provided with apertures 12 and 13 within which are enclosed certain hydrostatic devices for extending a detonator within a booster charge and controlling the operation of a clock mechanism respectively. The mine is also provided with a suitable cover 14 secured to the casing as by the bolts 15, a suitable gasket 16 being arranged between the cover and the casing to insure a watertight connection therebetween.

Within the aperture 12 is disposed the hydrostatic mechanism comprising a shaft 17 slideably supported within a bearing 18 to which is secured a flexible diaphragm 19 as by the bolts 21, a suitable annular member 22 being inserted between the heads of the bolts and the flexible diaphragm to provide a waterweight connection between the diaphragm and the casing of the mine. The shaft 17 is provided with a collar 23 secured thereto, by means of which the diaphragm 19 is held in clamped position by the nut 24 and the washer 25. A soluble Washer 26 of material suitable for the purpose such, for example, as a composition of salt, glycerin, and glue or the like, is secured to the shaft 17 as by the nut 27 and washer 28. The soluble washer is adapted to engage a shoulder 29 within the aperture 12 and thereby prevent movement of the hydrostat until the soluble washer has been dissolved or softened sufliciently to allow the pressure of the water against the diaphragm 19 to overcome the pressure of the spring 31 and move the detonating device 32 within the booster charge 33 whereby the detonator is effective to explode the booster charge.

The clock hydrostat comprises a flexible diaphragm 34 disposed within the aperture 13 and secured to the casing of the mine as by the bolts 35. An annular member 36 is disposed preferably between the heads of the bolts and the diaphragm to insure a watertight connection between the diaphragm and the casing of the mine. A shaft 37 is slideably supported within the bearing 38 and provided with a disc like portion 39 maintained in continuous contact with the diaphragm by the spring 41. When the mine has been planted-within a body of water of depth sufficient to cause the diaphragm to move the shaft 37 against the pressure of the spring 41, a clock mechanism indicated generally by the numeral 42 is set in operation. The mine is also provided with a chamber 43 Within which is disposed a firing relay indicated generally by the numeral 44 secured thereto as by a bracket 45. The chamber 43 is in communication with the detonator 32 by a tubular member 46 extending therebetween within which is disposed an electric cable 47. A battery BA is arranged within the chamber 48, a protecting pad or cushion 49 of material suitable for the purpose such, for example, as sponge rubber is provided to insulate the battery from the casing and protect the battery from excessive shock as the mine is launched. The firing control mechanism indicated generally by the numeral 51 is encased within a resilient pad or cushion 52 thereby to protect the mine firing mechanism from injury as the result of the violent shock received when the mine is launched. The firing control mechanism is in electrical connection with the cable 53 extending to a connecting box 54 within which the connections between the mine firing control mechanism, the relay 44, the detonator 32, the clock 42 and the battery are established, the electric cables 55, 56, and the cable conductors 57 being provided for this purpose. The mine casing is also provided with a chamber 58 filled with an explosive 59 suitable for the purpose such, for example, as an explosive known as TNT.

On Fig. 2 is shown a plan view of the mine firing mechanism with the upper cover thereof removed, the mechanism complising, among other elements, a supporting ring 61 provided with a plurality of apertures 62 therein adapted to receive the bolts 63, Fig. 3, provided with nuts 64 and washers 65 whereby the hemispherical covers 66 and 67 are securely clamped to the ring 61 thereby hermetically to seal the mine firing control mechanism by reason of the gaskets 68 and 69 arranged between the ring 61 and the covers 66 and 67, respectively.

The ring 61 is provided with a pair of diametrically arranged apertures 71 within which are disposed the supporting members 72 whereby the bearings 73 are supported in alined relationship with each other. Within the supporting members 72 are disposed the rods 74, insulated therefrom as by the insulating bushings 75 and securely maintained in the assembled position as by the nuts 76. An electrical connection is thus made from the conductors 77 and 78 to the spring members 79 and 81 respectively, clamped to the gimbal ring 82 as by the screws 83 and insulated therefrom as by the insulated bushings 84. The nuts 85 and 86 are provided for establishing an electrical connection between the conductors 87 and 88 and the springs 79 and 81, respectively. The

gimbal'ring- 82fis supported by the ball bearings 73 and additionally provided with a second pair of ball bearings 89 and 91, Fig.4, at a right angle to the axis of the bearings-73 whereby the platform 92 is supported on gimbals by reason of the supports 93 secured thereto and extendin'g'within the ball bearings 89 and 91. Within each of the supports is disposed a rod 94 and insulated therefrom as by the bushings 95 whereby the circuit from the conductors 87 and 88 is continued by way of 'the contact springs 80, rods 94 and the conductors 96 and 97 to the gravity controlled mine firing mechanism supported by the base 92. A suitable weight 98 is secured to the lower side ofth platform 92 as by the bolts 99 and washer 101, the bolts passing through apertures 102 within the supporting flange of the weight whereby the weight is adjustably mounted in a position to insure that the mine firingcontro'l mechanism will invariably assume a vertical position regardless of the position of the mine. The base or platform 92 is providedwith turned up portions'103 and 1 04 having bracing sections as 105, preferably securedto the horizontal portion of the platform as by welding .or brazing the parts together thereby to secure rigidity of the platform structure and to prevent bending or distortion of the same whereby the relative positions of the devices aifixed to the platform are maintained in predetermined spaced relation with each other. Secured to the base 92 as by the screws 106 is a reversible electric motor M provided with a gear 108 in meshed engagement with the gear 109 of the gear train indicated generally at 111, a shaft 112 having an offset member 113 thereon extends from the gear train mechanism and is adapted to be rotated in either direction in accordance with the direction of operation of the electric motor. Secured to the member 113 at one end thereof is a tapered torsional spring 114 clamped at the other end thereof to the support 115 as by the screw 116, the support 115 beingsecured to the base 92 in the manner illustrated; Secured to the central portionof the torsional spring 114 is a mirror 117 and-a boom 118 supporting a weight 119 affixed thereto'whereby the weight 119is pivotally mounted for a limited degree of rotative movement by the torsional spring114. Secured in spaced relation to the raised portion 103 of the base 92 as by the spacing members 120, the screws 121 and-washers 122, Figs. '6 and 7, is acl amping mechanism for preventing movement'of the boom 118 andweight 119 until after the mine is launched, the mechanism being mounted preferably upon an insulating plate 123 through which the screws 121 pass. The clamping mechanism comprises two arms 124 pivotally mounted on the studs 125 secured to the plate 123 as by the nuts 126 and maintained in pivoted relation thereto as by the screw 127 and washer 128. The arms 124 are urged apart at one end thereof by a retractile spring 129 whereby'a pair of clamping blocks 131 of insulating material such as hard rubber, phenol fiber or the like having a recessed portion 132 therein adapted to receive and clamp the boom 118 and be moved outwardly by the spring 129 when the fuse element 133 operates. The blocks 131 are secured to the arms 124 in any suitable manner as by the screws 134 illustrated. The outward movement of the blocks 131 is arrested by the stop pins 135 whichare engaged by the arms 124 when the fuse element 133 operates.

The fuse element 133 is clamped between the plates 136 and 137 by the screws 138, the plates 136 being secured to the members 139 as by the rivets 140. The members 139 are composed preferably of insulating material suitable for the purpose, such for example, as rubber or phenol fiber and secured to the arm 124 as by the screws 150. A pair of contactor screws 141 are threaded into the insulated plate 123 thereby to maintain an electrical connection between the conductors 142 and 143 and the plates 136and 137 respectively, by means of the conductors 144 and 145 of sufiicient flexibility to permit movement of the arms 124 when the fuse 133 operates, the flexible conductors 144 and 145 being secured to the plates 136 as by the screws 146. Secured to the insulated blocks 139 are two contact springs and 107 respectively, adapted to be brought into electrical engagement with each other and connected to the terminal screws and 170 for maintaining an electrical,

circuit between the terminal screws 110 and 170 by means of the flexible conductors provided and adapted to be disengaged from each other and thereby interrupt the circuit between the terminals 110 and 170 as the contact arms 124 move into engagement with the back stops in response to the operation of the fuse element 133.

Secured to the base 92 as by the bolts 147 is a projector 148 comprising an electrical bulb 149 which may be either of the incandescent or of the glow discharge type such, for example, as a bulb filled with neon, argon, hydrogen, or any other inert gas suitable for the purpose, and an potical system indicated generally at 151 adapted to focus the rays of light from the electric bulb on the mirror 117. The light reflected from the mirror 117 passes preferably through a lens 152 whereby the rays of light are caused to be focused upon the photronic cell 153 in'accordance with the angular position of the mirror. The projector 151 is arranged to emit a thin band of light byreason of a slit within a mask through which the rays of light pass or by reason of a straight line filament 154 employed with the incandescent bulb and arranged generally in the manner illustrated.

Asis well known, the photronic or photovoltaic cell comprises a thin metallic disc coated with a filament of sensitive material sealed in a moisture proof case with a glass window and provided with suitable terminals for establishing an external electrical connection thereto. The photro-nic cell employed with the present invention is provided with two films of sensitive material separated by a band or space 237, Fig. 9, within which the rays of light are adapted to be focused when the mirror 117 and weight'119 are in the adjusted position. When the light rays are moved upward from the space 237, an electricalpotential is generated between the terminals 155 and 156 and, when the reflected rays are moved downward from the space 237 an electrical potential is generated between the terminals 155 and 157, as will more clearly appear as the description proceeds. Two sensitive relays D and MG are connected to the terminals of the photronic cell and adapted to be operated selectively by electrical currents generated variably by the photronic cell in accordance with the movement and position of the beam of light engaging the photronic cell as the result of angular movements of the mirror 1 17 and weight 119. The relay MG is provided with two windings and a highly damped armature adapted to be moved to circuit closing position in response to a current of predetermined strength flowing through either relay winding for a. predetermined period of time. There are also provided two relays indicated generally by the letters E and F adapted to be operated selectively in accordance with the openated condition of relay D thereby to cause the motor M tobe operated forwardly or reversely, as the case may be, and thus vary the torsion of the spring 114.

There is also provided a clock 217 secured to the base 92 and having a plurality of contacts operable in pre-- in response to the'energization of the electromagnet and again closed its contacts after a delay of substantially four hours. Contact C closes as armature 160 moves from an initial position in response to the energization of the electromagnet and disengages after substantially four hours has elapsed.

Referring now to Fig. 8 of the drawings, the pendulum 159 is shown thereon somewhat in detail, the pendulum comprising a casing 162 fitted at the upper end thereof with an insulating bushing 163 maintained in position as by the screw 164. The bushing is preferably threaded to receive a metallic insert 165 held securely in the assembled position as by the nut 166 thereon. Within the insert 165 is threaded a screw member 167 having an aperture 168 within the lower end thereof and provided with a pair of nuts 169 adapted for electrical connection with the conductor 171 as by the terminal 172. The insert 165 is provided with a lower projecting arm 173 having secured thereto a pivot bearing 174 adapted to receive a pivot 175 having a projecting portion 176 disposed within the aperture 168 and connected to a supporting frame 177 as by the nuts 178. The projecting portion 173 is provided with a stud 179 to which is affixed one end of a resilient coiled spring 181 having the other end thereof secured to the supporting frame 177. Suspended from the supportnig frame and secured thereto as by the nuts 182 is a plunger rod 183 loosely fitted within a sleeve 184 and provided with a resilient spring 185 whereby the weight of the pendulum bob 186 is yieldably supported by the spring 185. The bob is provided preferably with an annular member 187 of suitable yieldable material such, for example, as soft rubber adapted to absorb the shock of impact of the pendulum bob against the inside of the casing 162 during the launching of the mine. Secured to the inner portion of the sleeve 184 is a flexible wire or rod 188 having an extended portion 189 preferably of precious metal such, for example, as silver or gold connected thereto as by the coupling 191 and adapted to engage the precious metal sleeve 192 supported by the insert 193 within the bushing 194 secured to the casing 162. The insert 193 is provided with a screw 195 passing through an aperture within the casing and electrically insulated therefrom as by the bushing 196, the nut 197 being provided for the purpose of preventing movement of the insert 193 with respect to the casing. A nut 198 is provided for the purpose of establishing an electrical connection between the screw 195 and the conductor 201. A cap 202 having a transparent disc 203 preferably mounted therein is threaded into the lower end of the casing 162 thereby to prevent the entrance of dirt or moisture within the casing and thus maintain the electrical contact surfaces in a condition of high electrical conductivity.

The pendulum is secured to the base 92 in any suitable manner as by the supports 204 securely clamped to the port-ion 104 of the case as by the bolts 205, the bolts 206 being provided for clamping the pendulum to the support in a vertical position.

Referring now to Fig. 9, the clock 42 shown thereon comprises a spring motor 207 for actuating a train of gears including an escapement mechanism adapted to be set in operation as the plunger P is actuated by movement of the rod 37 of the clock hydrostat in response to the pressure of the water against the diaphragm 39. The clock also includes a cam member 208 adapted to actuate the contacts G and H to closed position after the clock has been in operation for a suitable period of time such, for example, as three hours. The cam 208 is provided preferably with an arcuate slotted portion 209 within which is disposed the stop pin 211 thereby to arrest the movement of the cam 208 and maintain the contacts G and H in closed position after the contacts have been actuated.

The operation of the system will best be understood by consideration of the circuit diagram of Fig. 9 on which is shown a battery BA adapted to be operatively connected to the mine firing control mechanism in response to the closure of cam contacts G and H of the clock mechanism 42. When this occurs, battery is applied to the mine firing control mechanism by way of the gimbal contacts GCl and to the winding and armature of the firing relay 44 thereby setting into operation certain timing and control devices to cause the mine to assume an armed condition after a predetermined period of time has elapsed, as will more clearly appear as the description proceeds.

Let is be assumed, by way of example, that the mine has been launched within a body of water of sufficient depth to cause the clock hydrostat to operate and set the escapement mechanism of the clock 42 in operation and that the mine has been launched for a sufficient period of time to permit the soluble washer 22 to dissolve or become softened sufiiciently to permit the detonator 32 to be inserted within the booster charge 33 by the pressure of the water on the flexible diaphragm 19. Let it be further assumed that the boom 118 and weight 119 are held in clamped position by the fuse element 133 thereby to prevent damage or injury to the gravitational detecting device during the handling and planting of the mine.

When the mine has been launched for a period of time sufficient to allow the contacts G and H to be closed by the cam 208 of the clock 42, ground at cam H is applied by way of conductor 212 to one terminal of the battery BA from whence the circuit is continued by way of the other terminal of battery BA, conductor 213, contact G, conductor 214, gimbal contacts GCl, conductor 215, contacts 107 and 100, conductor 216, winding of the electromagnet of the clock mechanism 217, conductor 218, fuse 133 and thence to ground, the fuse 133 being shunted by contact A of the clock mechanism and for this reason the fuse does not operate until contact A opens. The application of battery potential to conductor 215 as contacts G and H are closed by the earn 208 causes the electric bulb 149 to be lighted and thus a source of light is provided for the selective energization of the Photronic cell 153.

The electromagnet attracts the armature 160 thereby winding the clock and causing contacts A and B to be disengaged and contact C to be closed. The disengagement of contact A causes the current through the winding of the electromagnet to flow through the fuse 133 thereby operating the fuse and releasing the arms 124 of the clamping mechanism. The disengagement of the cam B contact interrupts the circuit to relay 44 thereby preventing the premature detonation of the mine. The closure of the cam C establishes a circuit connection from conductor 215 to the winding of the electromagnet of the clock 217 whereby the clock continues to wind at six minute intervals until a period of four hours has elapsed, at which time the contact C is opened and the clock is brought to rest. When the fuse element 133 operates, the circuit to the electromagnet of the clock is interrupted and the armature 160 thereof is actuated by a retractile spring to the initial position of the armature, as is well known in devices of this character, at which time contact A closes thereby causing the clock to rewind. Contact B, it will be noted, does not close until a period of four hours has elapsed thereby interrupting the circuit to the firing relay 44 until a sufficient time has elapsed to allow the weight 119 and mirror 117 to come to rest in the adjusted position.

As the arms 124 of the clamping mechanism are moved by the retractile spring 129 into engagement with the back stops 135, spring 107 is disengaged from spring thereby transferring the control of the clock winding mechanism from the clamping mechanism to contact C and the clock is thus brought to rest when contact C opens at the expiration of a predetermined period of time such as four hours.

Let it be further assumed that a degree of torsion has been applied to the spring 114 by the member 113 insutficient to prevent the rotary movement of the weight 119 downwardly by the gravitionalforce acting-thereon;

therebyto cause the boom 118 to be arrested by the block 131 secured to'the lower arm 124 and the mirror 117 to be tilted in such a manner 'as to cause the focused rays of the electric bulb 149 to fall upon the uppersensitized portion of the photronic cell thereby setting up an electrical potential between the terminals 155 and 156 there of. A current is now caused to'fiow through the followingcircuit: i i 1 4 Terminal 155, conductor 219, winding 2 of relay D; conductor 221, winding 1 of relay MG in parallel with the resistance element .222, conductor 223 and thence to terminal 156 thereby causing relays D and MG to operate. As armature 224 of relay D moves into engagement with contact 225,. ground is applied to conductor 226, winding of relay E, conductor 215, contacts GCI, conductor 214, contact G, conductor 213, battery BA, conductor 212, contact H and thence to ground, thereby causing relay E to'operate. The operatio'n" of relay MG at this time is without eifect as the circuit to the contacts of armature 246 thereof is interrupted at contact B.

Thebperatioh of relay E' atarmature 227 thereof applies battery by way of conductor 228 to the field winding FW of the motor M, the circuit continuing to ground. The field winding ofthe motor is thus energized. .As armature 229 of relay E moves into engagement with its make contact, battery is applied by way of conductor 231, brush 232, armature of the motor M and brush 233 thereof, conductor 234, make contact and armature 235 of relay E and thence to ground thereby causing the motor to be operated in a direction to increase the tension'of the spring 114 and move the boom 118 and weight 119 upward against the force of terrestrial gravitation and away from the lower block 131, Fig. 6, of the clamping mechanism. As the motor'continues to operate, additional tension is applied to the spring 1'14,by the gear train 111 and offset member 113 until the boom and weight have been moved angularly to a predetermined position of equilibrium intermediate the upper and lower blocks 131, thereby causing the focused rays of light to be shifted, from the upper sensitized portion of the Photronic cell to the position illustrated on Fig. 9 intermediate the upper and lower' sensitized portions of the cell. When this occurs the electromotive force generated by the Photroniccell at the terminals 155 and l56 thereof is reduced sufiiciently to release relay MG and cause armature 224 of relay D to be moved to a null position intermediate the contacts 225 and 236.

As armature 224 moves away from contact 225, ground is removed from relay E thereby causing relay-E to release and interrupt the operating circuit to the motor M. The motor. M is thus brought to rest with the gravitational detecting element 119 in an adjusted position'such that the focused rays of light reflected from the mirror 117 engage the space indicated generally at 237 between the upper and lower sensitized portions of the Photronic cell 153.

In the event that the initial tension applied to the spring 114 is sufiicient to move the boom 118 and weight 119 upwardly against the force ofgravity into engagement with the upper clamping block 131 as the arms 124 are released, the focused rays of light are reflected downward into engagement with the lower sensitized portion of the Photronic cell thereby setting up an electromotive force between the terminals- 155 and 157 sufficient to cause the operation of relays D 'and MG over the following circuit:

Terminal 155, conductor 219, winding 1 ofrelay D, conductor 238, winding 2-of relay MG in parallel with resistance element 239, conductor 241 and thenceto terminal 157. The operation of relay D by the energizationof the winding 1 thereof causes armature 224 there of to move intoengagement with contact 236 and thereby.

gimbal contacts G Cl, conductor 214, contact G, conductor 213,-bat-tery BA, conductor'212, contact'H and thence to ground thereby causing relay F to operate and at armature 243 and make Contact thereof apply battery by .way of conductor 228 to the field winding FW of the motor-and thus energize the field winding. The operation of relay F at armature 244 and make contact there-- of applies battery to conductor 234, brush 233, armature ofthe motor M, brush 232, conductor 231, make contact and armature 245 of relay F from whence the circuit is justedposition such that the focused rays of ilight-fall within the portion 237 of-the Photronic cell. a -When thisoccurs insufficient electromotiveforce is generated between the terminals and 157 to maintain relay D operated and armature 224 thereof moves away from con-' tact 236 thereby interrupting-the circuit to the Wind-1 ing of relay F and causing relay F to release and bring the motor to rest with the boom and weight in the adjusted position such that the focused rays of-lightfall within the space 237 of the Photronic cell. As the rays of light engage the portion 237 of the Photronic cell, relay -MG releases.

As the mirror and weight move from theadjusted'position in response to the release of the arms 124,- the electromotive force generated between the terminals 155 and 1-56, or 155 and 157, as the case may be, is sufficient to cause the operation of the relay D and the marginal relay MG. As the grounded armature 246 of relay MG moves into engagement with either of its make contacts, ground is applied by way of conductor 247 to contactB of the clock 217, but contact'B, it

will be recalled, is in an open condition and the operation of relay MG a't-this time is, therefore, without effect.

As the focused beam of light is moved into the adjusted position in engagement with the section 237 of-th'e Photronic cell, relay MG releases thereby removing ground from conductor247.

The mannerin which the mechanism is adapted to compensate for relatively slow variations in the'force 'of terrestrial gravitation due to the rise and fall of tides and the like will now be described. The optical system employed with the' present invention is adapted to reflect a beam of light angularly in accordance with the instant position of the'gravitational responsive element, a Photronic cell being disposed within the path of travel of the focused beam of light. When the rays of light fall upon the slotted portion 237 intermediate the upper and lower sensitized surfaces of the Photronic cell, the electromotive force generated between the pair of terminals 156 and 155 or thepair of terminals 157- and 155, as the case may be, is insuflicient to cause the operation of relays D and MG. As the rays of focused light are movedaway' the upper and lower sensitized portions of the Photronic' cell. A flow of current is thus set up in the windings of relay D and MG, the current through the winding of relay MG being somewhat less than the current through the winding of relay 'D by reason of the resistance elements 222 and 239 connected in parallel with windings 1 and 2 respectively of relay MG. Thus, for a relatively shortmovement of the beam of light away from the null position such as may be occasioned by changes in the weight of the bodyof water as the result of the gravitational influence of tides or as the result of a change in the density of the surrounding mass such, for example, as may be occasioned by the moyementof small craft within the;

vicinity of the mine, the movement of the beam of light from the null position is sufficiently slow to cause relay D to operate and set the motor in operation to vary the tension in the spring 114 and thus compensate for the change in the gravitational force acting on the weight 119, before the beam of light has been moved sufliciently from the null position to cause relay MG to operate. The current flowing through the winding of relay D is decreased sufficiently to cause relay D to release when the variation in the gravitational force acting on the mass 119 is balanced by the spring 114 such that the weight 119 is adjusted to a position in which the reflected beam of light engages the portion 237 of the Photronic cell. An arrangement is thus provided in which small gravitational effects are continually balanced by the selective operation of the motor M thereby maintaining the weight 119 in a predetermined adjusted position.

When a ponderous mass such, for example, as a vessel approaches within the vicinity of the mine, the weight 119 thereof is moved downward by reason of an increase in the gravitational force acting thereon. It is the usual practice to construct vessels such that the center of gravity of the vessel is some distance above the center of buoyancy of the displaced water and, for this reason, the gravitational force under such a vessel is greater than the gravitational force at a corresponding depth of submersion within the surrounding water. As the weight 119 moves downward the mirror 117 is moved angularly to a position in which the reflected rays of light from the electric bulb 149 engage the upper sensitized portion of the Photronic cell. This action occurs more quickly than the rate at which compensation for this change in the gravitational force can be effected by the motor by reason of the gear train 111 employed between the motor M and the offset member 113, and thus the beam of light moves upward a distance from the divided portion 237 of the Photronic cell to generate an electromotive force between the terminals 155 and 156 thereof suflicient to cause the operation of relay MG in addition to relay D.

As armature 246 of relay MG moves into engagement with the make contact thereof, ground is applied to conductor 247, contact B, conductor 248, gimbal contacts GC2, conductor 249, winding of relay 44 from whence the circuit is continued by way of conductor 214, contact G, conductor 213, battery BA, conductor 212 and cam H to ground. Relay 44 is a slow-to-operate relay by reason of a copper slug disposed about the core of the relay magnet or by reason of any similar device suitable for the purpose such, for example, as a dash pot, or escapement mechanism connected thereto and thus the energizing current is required to flow through the winding of the relay for a predetermined time before the relay operates. As armature 241 of relay 44 moves into engagement with the make contact thereof, a circuit is closed from ground at cam H, conductor 212, battery BA, conductor 213, contact G, conductor 214, armature 251 and make contact of relay 44, conductor 252 and thence to one terminal of the detonator device 32 having the other terminal thereof connected to ground thereby causing the detonator to operate and explode the mine beneath a vulnerable portion of the vessel.

Whereas in the illustrative embodiment of the invention disclosed on the drawings, a slow-to-operate relay 44 is employed to close a circuit to the detonating device in response to the operation of relay MG, it will be understood that this is shown and described for illustrative purposes only and that other suitable time delay devices such, for example, as dash pot controlled devices, clock escapement mechanisms and the like may be employed for introducing a predetermined time delay in the closure of the circuit to the detonating device without departing from the spirit or scope of the present invention.

In the event that the mine is disturbed by a shock or pressure impulse such, for example, as may be received as a result of a countermining operation, sufiicient to cause the pendulum device 159 to operate, the contact element 189 thereof moves into circuit closing position thereby closing a circuit from ground at cam H by way of conductor 212, battery BA, conductor 213, contact G, conductor 214, gimbal contacts GCl, conductor 215, pendulum contacts 189, conductor 216, winding of the electromagnet of the clock 158, contact A and thence to ground thereby causing the electromagnet to be energized and operate the pivoted armature 160. As armature 160 moves from its initial or home position, contacts A and B are opened and contact C is closed. As contact B moves to open position, the operate circuit to the relay device 44 is interrupted thereby preventing the operation of relay 44 as the result of vibrations or oscillations of the gravitational responsive element during the time that contact B remains open.

Cont-act B, it will be recalled, does not close until a period of time such as four hours has elapsed and therefore there is no possibility of prematurely detonating the mine for a period of at least four hours after the first shock or pressure impulse has been deceived. The closure of cam C completes a circuit from battery at conductor 215 to one end of the electromagnet of the clock 217 whereby the electromagnet is repeatedly energized at six minute intervals in response to the repeated closure of cam A each time the armature 160- returns to the unoperated position. At the expiration of the four hour eriod hereinbefore referred to, cam C contact opens thereby preventing re-energization of the electromagnet in response to the closure of cam A as the armature 160 returns to the unoperated position and thus causing the clock to come to rest with the contact C in the open position and contacts. A and B closed.

In the event that the mine is subjected to vibrations of small amplitude such, for example, as may be produced by tremors of the earth caused by countermining operations at a considerable distance from the mine which are insuflicient to cause the pendulum device to operate and move the contact element 189 thereof to closed position, but of suflicient amplitude to set the boom 118 and mass 119 into oscillation, such vibrations will ordinarily occur at a frequency relatively high with respect to the natural frequency of the suspended boom and mass and will, therefore, rarely if ever, actuate the suspended mass resonantly at its natural rate of vibration. If the amplitude of the vibrations of the mass or period of the vibrations should be :sufliciently large as to cause the current generated by the Photronic cell to be increased to a value such as would cause movement of the armature 246 of relay MG from the null or rest position thereof, the duration of the continuous flow of the current will be relatively brief as the result of the vibrating condition of the mass and mirror 117, and the relay MG will, therefore, not receive electrical impulses of suflicient duration to cause the relay to operate by reason of the highly damped armature employed and by reason of the'arrangement of the electrical contacts which are preferably adjusted such that the armature is required to be moved through a considerable distance from the null or unoperated position to engage the same.

Furthermore, the vibrations of the mass and mirror cause the upper and lower sensitized portions of the Photronic cell to be activated whereby the damped armature 246 of relay MG is urged alternately in opposite directions by the successive energization of windings 1 and 2 respectively of the relay and thus the armature is eifectively prevented from moving a sufiicient distance from the null or unoperated position thereof to engage either of its make contacts. The stop pins are so arranged that the arms 124 move through a small angular distance before they are arrested by the stop pins and the degree of angular movement of the boom and weight 119 is thereby limited to a small amount by the clamping blocks 131 which limit the angular movement of 13 the rn-irror' 117 to a :predetermined amount-whereby the reflectedrays of focused light are controlled in such a manner asrto prevent the flow of anexcess of electric current through the .windings of the relay MG in response to the. activation of thePhotronic cell.

.An-arrangement is thus provided in which fortuitous vibrations ;of the gravitational element of insuflicient strength to close the pendulum contacts maycause electrical'currents to flow repeatedly through the windings of thefiring control relay MG for varying: periods of time up to several seconds each or for a period of time comparable to or in excess of the natural period of vibration of theboom and 'mass without causing the armature 246 of :relay MG tou be moved into engagementwith either of its make contacts. Premature detonation'of the mine by countermining operations or other vibrations o disturbances is thus positively prevented.

Briefiy stated in summary, the present invention pro-- vides new and improved means for. controlling a mine firing mechanism in which the force of. gravity is employed to'controlthe firing mechanism and explode the mine upon the approach of a: ponderous mass such, for

example, as a yes'sel, and in which compensation is auto-. matically made for continuallymaintaining the gravita'-' tional responsive detecting element ina predetermined position regardless of the gravitational changes within the body of water-within which the mine is planted caused by tides or'movements of small craft within the vicinity of the mine. Furthermore, means are provided for effectively preventing-premature detonation of the mine as the result of disturbances produced by countermining operations.

-While the invention has been describedwith respect to a certain preferred example thereof which gives satisfactory results, it will be understood bythose skilled in the art to whichthe invention pertains, after understanding the invention, that'various changes and modifications may be made, and various instrumentalities may be employed without departing'from the spirit and scope of theinvention, and it' is my intention, therefore, to cover in the appended claims all such changes, modifications, and instrumentalities.

a The invention herein described may be manufactured and used by or for theGovernment of the United States of America for governmental purposes without the payment of any'royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A gravitational responsive device having a movable element responsive to changes-in the terrestrial gravitational field adjacentthereto, means for yieldably support-' ing said element for rotativemdvement about a honzontal axis, means for yieldably setting said element to an initial position, motivemeans controlled by the element for automatically adjusting said setting means to compensate for variations in the gravitational pull on said element caused by a predetermined rate of change in either direction in the strength of said terrestrial gravitational field, and means controlled by the element and constructed and arranged to operate an electro-responsive detonating device when the strength of said gravitational fieldvaries in excess of said predetermined rate of change.

2. A gravitational responsive device having a movable element responsive to changes in the terrestrial gravitational field adjacent thereto, means for yieldably supporting said element for rotative movement about a horizontal axis, means for yieldably setting said element to an initial position, means controlled by the element for automatically adjusting said setting means to compensate for variations in the gravitational pull on said element caused by a predetermined rate of change in either direction in the strength of said terrestrial gravitational field, an electro-responsive detonating device, and means controlled by the element for causing said electro-responsive detonating the bed, of a bodyof water adjacent the path of a vessel,

a movable element adapted to be actuated in either di-. rection from an initial position selectively in response to changes in the terrestrial gravitational field adjacent thereto, means for yieldablysupporting said element for rotative movement about a horizontal axis, means for releasably locking said element in said initial position, a timing mechanism, means for setting the timing mechanism in operation after the mine has been planted, means controlled by saidvtirning mechanism for releasing said locking means for movement about said axis, means controlled by said element selectively in accordance with the direction of movement thereof from said initial position and effective when said releasing means has been released for adjusting said supporting means to yieldably set the element to said initial position, and means including an electro-responsive device for closing an electrical circuit when said movable element is rotated a predetermined distance from said initial position by a predetermined change in the strength of said terrestrial gravitational field. 1 Y

4. In a gravitational responsive device of the character disclosed, a movable element responsive to variations in.

the gravitational field adjacent thereto, means for yieldably supporting said element for rotative movement about a horizontal axis, means for automatically adjusting said supporting means to compensatefor slow variations in,

said gravitational field, a detonating device, and means for operating said detonating device when said element has moved'through a predetermined angular distance in -response to a relatively rapid variationin'said gravitational field.

5. In a gravitational device of the character disclosed, a movable element responsive to variations in the strength of the gravitational field adjacent thereto, means for yield ably supporting said element for rotative movement in either direction from an initial position about a horizontal.

itational element adapted to be moved to different positions by variations inttheterrestrial gravitational field within which the mine is disposed, means for yieldably supporting said gravitational element for movement about a an axis, means including a reversible motor for balancing said gravitational element in an initial position against the force of terrestrialgravitation, means controlled by the gravitational element for selectively operating said reversible motor thereby to-prevent movement of said gravitational element beyond a predetermined distance from said initial position in response .to small predetermined variations in said gravitational field, and means controlled by said gravitational element for causing the mine firing mechanism to fire the mine when the gravitational element has moved beyond said predetermined distance from said itational element adapted to .be moved to different positions by variations in the terrestrial gravitational field within which the mine is disposed, means for yieldablysupporting said gravitational element for movement about an axis, means including an electro-responsive device for balancing said gravitational element in an initial position against the force of terrestrial gravitation, means controlled by the gravitational element for selectively operating said electro-responsive device thereby to prevent movement of said gravitational element beyond a predetermined distance from said initial position in response to relatively slow changes in the weight of said gravitational element caused by variations in said gravitational field, and means for causing the mine firing mechanism to fire the mine when said gravitational element has moved beyond said predetermined distance from the initial position in response to more rapid changes in the weight of the gravitational element caused by the movement of a ponderous mass within the-vicinity of the mine.

8. In a submarine mine of the character disclosed arranged on the bed of a body of water adjacent the path of travel of a vessel, mine firing mechanism comprising a movable weight adapted to be actuated to different settings in accordance with variations in the strength in the terrestrial gravitational field adjacent thereto, means for pivotally supporting said weight for rotation about a horizontal axis, means for applying a varying degree of torsion to said weight supporting means thereby to cornpensate for relatively slow changes in the strength of said gravitational field, releasable means for rigidly securing said weight during the planting of the mine, means controlled by the pressure of the body of water for causing the weight supporting means to be released from the weight securing means, a source of light, means for focusing the light rays from said source, means for reflecting the focused rays in accordance with the settings of said weight, a light responsive device arranged within the path of travel of the focused rays of light reflected by said reflecting means and adapted-to generate a variable electromotive'force in accordance with the instant position of the rays of light reflected by said reflecting means, a relay mechanism operatively connected to said light responsive device and adapted to be operated selectively in accordance with the electromotive force generated by the device, and mine firing means adapted to be operated by said relay mechanism when said focused rays of light engage a predetermined portion of said light responsive device.

9. In a submarine mine of the character disclosed arranged within the terrestrial gravitational field adjacent the path of travel of a vessel, detecting means including a mass adapted to be attracted variably in accordance with the strength of said gravitational field, means for yieldably supporting said mass in a predetermined position for rotation about a horizontal axis, an electro-responsive device, a source of variable electrical energy operatively connected to said electro-responsive device, means for controlling the energy from said source selectively in accordance with the instant position of said mass, detonating means, and means controlled by said electro-responsive device for causing the mine to be fired by said detonating means when the energy from said source has been increased to a predetermined value.

10. A mine firing mechanism of the character disclosed arranged within a gravitational field comprising in combination, a timing device operable in unit cycles, a pair of normally closed contact elements included in said timing device and adapted to be disengaged during said unit cycles of operation, gravitational detecting means movable variably to different positions in accordance with variations in said gravitational field, a source of light, light reflecting means controlled by said detecting means and arranged within the path of travel of said light, a light responsive electrical generating device adapted to be activated selectively by light reflected from said reflecting means as the detecting means moves to said diflerent positions for generating electrical energy variably in accordance with the portion of the light responsive device engaged by the reflected light, means including a relay controlled by said light responsive device for maintaining the engagement of said light continuously with a predetermined portion of said light responsive device when relatively slow gravitational changes are detected by the detecting device, a firing circuit including the normally closed contact elements of said timing device, relay means operatively connected to said light responsive device and adapted to close said firing circuit when the gravitational detecting means is set to a position such that the light reflected by said light reflecting means engages another predetermined portion of said light responsive device when more rapid changes in the gravitational field are detected by the detecting device, and means responsive to a disturbance of said mine firing mechanism for causing said firing circuit to be interrupted by said timing device.

11. In a submarine mine of the character disclosed ar-,

ranged on the bed of a body of water within the gravitational field adjacent the path of travel of a vessel, detecting means including a mass adapted to be attracted variably in accordance with the strength of said gravitational field, means for releasably clamping said mass in a predetermined position, means including a device controlled by the pressure of the water for releasing said clamping means, means effective when the clarnping means has been released for yieldably supporting said mass in said predetermined position for-rotation about a horizontal axis, an electro-responsive device, a source of variable electrical energy operatively connected to said electroresponsive device, means for controlling the energy from said source selectively in accordance with the instant position of said mass, detonating means, and means controlled by said electro-responsive device for causing the mine to be fired by said detonating means when the energy from said source has been increased to a predetermined value.

12. In a gravitational responsive device of the character disclosed, a source of electrical current, means including a yieldably supported mass for controlling said current variably in accordance with changes in the strength of the gravitational field Within which the device is disposed, means including an electro-responsive device controlled by said current for causing the mass to be yieldably maintained in a predetermined position regardless of relatively slow changes in the strength of said gravitational field, an explosive charge, detonating means, and means operatively connected to said source of electrical current for causing the detonating means to fire the explosive charge whenthe current has reached a predetermined value in response to the movement of said mass beyond said predetermined position by more rapid changes in the strength of the gravitational field.

13. In a system of the character disclosed for detecting changes in the terrestrial magnetic field adjacent thereto, a yieldably supported mass adapted to be moved about a horizontal axis in either direction from an initial position by variations in the force of gravitational attraction acting thereon, means for applying a force to said mass suflicient to balance said force of gravitational attraction, means controlled by the mass in accordance with the degree of movement thereof from said initial position for varying said force at a predetermined rate, means effective when gravitational changes are detected by said mass at a rate not to exceed the rate at which the balancing force is applied for continually maintaining the mass at said initial position, a load circuit, and means including an electro-responsive device for closing said load circuit when the mass is additionally moved a predetermined distance from the initial position by gravitational changes at a rate faster than the rate at which the balancing force is applied thereto.

14. In a gravitational detecting mechanism comprising a mass adapted to be actuated to different positions in response to variations in the gravitational force acting thereon, a source of light, means controlled by said mass for reflecting the light from said source along a path of travel, a Iphotronic cell disposed within the path of travel of said light and adapted to generate electrical energy variably in accordance with the instant position of the reflected light, means controlled by said photronic cell for continually maintaining said mass in an initial position when the changes in saidgravitati'onal force are small, and means operatively connected to said photronic cell for closing an electrical circuit when the changes in said gravitational force are sutficiently large to cause the mass to be actuated beyond a predetermined distance from said initial position.

15. A firing mechanism of the character disclosed arranged within a gravitational field comprising a mass adapted to be actuated to different positions in accordance with variations in the strength of said gravitational field, a pair of pivoted members adapted to clamp said mass in an initial position, a fusible device for maintaining said pivoted members in the clamping position, a source of electrical power, means for causing said fusible device to be connected to said source of power thereby to operate the fusible device and release the pivoted members, an electro-responsive timing mechanism having a pair of normally closed contacts adapted to open for a predetermined period of time as the timing mechanism operates, a control circuit for said electro-responsive timing mechanism, means controlled by said pivoted members for interrupting said control circuit as the pivoted members are released, means including a resilient member for yieldably supporting said mass for angular movement about an axis as said pivoted members are released, a photronic cell, means for activating the photronic cell selectively in accordance with the degree of movement of said mass, means controlled by said photronic cell for adjusting said yieldable supporting means to maintain said mass continually in a predetermined initial position as small changes in the gravitational field are detected by the mass, a load circuit including said normally closed contacts of the timing mechanism, and means controlled by said photronic cell in response to a predetermined degree of movement of said mass from said initial position for closing said load circuit.

'16. In a firing mechanism for a submarine mine adapted to be laid on the bed of a body of water, the combination of a photronic cell having two divided sensitized portions adapted to be activated by rays of light, a source of light, a gravitationally responsive device having means for directing the light from said source upon the photronic cell selectively in accordance with variations in the terrestrial gravitational field adjacent thereto, a null portion of said photronic cell intermediate said two sensitized portions, means for maintaining the directed light upon said null portion of the photronic cell when the variations in said gravitational field to not exceed a predetermined amount, and means for directing the light upon the upper and lower portions of the photronic cell selectively when the variations in said gravitational field exceed said predetermined amount.

17. In a submarine mine of the character disclosed adapted to be laid on the bed of a body of water adjacent the path of travel of a vessel, gravitational detecting means comprising a movable mass adapted to respond to variations in the gravitational force acting thereon, means for compensating for small gradient variations in said gravitational force, and means controlled by the movable mass for causing the mine to explode in response to relatively large gradient variations in said gravitational force.

18. In a submarine mine adapted to be laid on the bed of a body of water adjacent the path of travel of a vessel, means including a movable mass for detecting changes in the gravitational field within which the mine is disposed, means for compensating for the gradient variations of weight of the mass due to gravitational changes brought about by the tides of the body of water, a detonating device, and means controlled by said detecting means for causing the detonating device to fire the mine when said 18 mass has moved a predetermined distance in response to relatively large gradient variations in the weight of the mass caused by the movement of the vessel within the vicinity of the mine.

19. In apparatus of the character disclosed arranged within the terrestrial gravitational field adjacent the path of travel of a vessel, the combination comprising a sub marine mine, a detonating device therefor, means for detecting variations in the strength of the gravitational field adjacent said mine, and means controlled by said detecting means for firing said detonating device when a variation in the strength of the gravitational field exceeds a predetermined value. 1

20. In apparatus of the character disclosed adapted to be laid on the bed of a body of water, the combination comprising a submarine mine, means responsive to the pressure of the water for arming the mine, means for detecting variations in the strength of the gravitational field adjacent the mine, and means controlled by said detecting means for causing the armed mine to explode when a variation in the strength of the gravitational field exceeds a predetermined value.

21. In an apparatus for firing a submarine mine adapted to be laid on a bed of a body of water adjacent the path of a vessel, a yieldably mounted gravitationally responsive element, means for balancing the element in a predetermined position, means including an electro-responsive device selectively controlled by said element for eftecting corrections in the balance of the element as small gradient changes in the gravitational force acting on said element are received, and means controlled by said elec-' tro-responsive device for firing the mine in response to relatively large gradient changes in said gravitational force.

22. In an apparatus for firing a submarine mine adapted to be laid on the bed of a body of water adjacent the path of a vessel, a movable mass, means for applying a force to the movable mass suficient to balance the terrestrial gravitational force acting thereon, means for preventing substantial movement of said mass in response to small gradient changes of said gravitational force, and means controlled by said mass forcausing the mine to explode in response to large gradient changes in the gravitational field caused by the approach of a vessel within the vicinity of the mine.

23. In an apparatus for control ling the firing of a submarine mine adapted to be laid on the bed of a body of water adjacent the path of a vessel, a yieldably mounted gravitationally responsive element, means for clamping the element in an initial predetermined position, means for releasing the element for movement about an axis in response to the launching of the mine within said body of water, means for applying a balancing force to said element sufficient to cause the element to be yieldably maintained in said initial position, means for controlling an electric circuit selectively in accordance with variations in either direction in the gravitational force acting on said element, and means controlled by said circuit for causing the mine to explode in response to a predetermined change in said gravitational force.

24. An apparatus for detecting gravitational changes which comprises a mass, means for yieldably supporting the mass for movement about a horizontal axis, means for applying a balancing force to said mass sufiicient to cause the mass to be yieldably adjusted to an initial position, means including a motor adapted to be operated selectively in either direction under control of said mass in accordance with the direction of movement of the mass from said initial position for automatically varying the balancing force applied to said mass sufficiently to compensate for variations in the weight of the mass as small gradient changes in either direction in the gravitational field are detected, and means controlled by said mass for causing a load circuit to be closed when said 19 gradient changes in the gravitataional field exceed a predetemiined value.

25. A gravitational responsive device having a movable element responsive to changes in the terrestrial gravitational field adjacent thereto, means for yieldably supporting said element for rotative movement about a horizontal axis, means for yieldably setting said elementto an initial position, an electro-responsive device comprising a pair of voltage generators adapted to be activated selectively by said element in accordance with the direction of movement thereof from said initial position, means including a motor adapted to be operated in either direction selectively in accordance with the activated one of said voltage generators for automatically adjusting said setting means to compensate for variations in the gravitational pull on said element caused by a predetermined rate of change in either direction in the strength of said terrestrial gravitational field, an electro-responsive detonating device, and means controlled by the element and constructed and arranged to operate said detonating device when the strength of said gravitational field varies in excess of said predetermined rate of change.

26. A gravitational responsive device having a movable element responsive to changes in the terrestrial gravitational field adjacent thereto, means for yieldably supporting said element for rotative movement about a horizontal axis, means for yieldably setting said element to an initial position, an electro-responsive device comprising a pair of voltage generators adapted to be activated selectively by said element in accordance with the direction of movement thereof from said initial position, means including a motor adapted to be operated in either direction selectively in accordance with the activated one of said voltage generators for automatically adjusting said setting means to compensate for variations in the gravitational pull on said element caused by a predetermined rate of change in either direction in the strength of said terrestrial gravitational field, an electro-responsive detonating device, and means controlled by the element for causing said electroresponsive detonating device to operate when the strength of said gravitational field varies in excess of said predetermined rate of change.

27. A gravitational responsive device having a movable element responsive to the changes in the terrestrial gravitational field adjacent thereto, means for yieldably supporting said element for rotative movement about a horizontal axis, means for yieldably setting said element to an initial position, said element setting means including a gear train, motive means including a reversible motor controlled by the element for driving the gear train selectively in either direction thereby to automatically adjust said setting means to compensate for variations in the gravitational pull on said element corresponding to a predetermined rate of change in either direction in the strength of said gravitational field.

28. A gravitational responsive device having a movable element responsive to the changes in the terrestrial gravitational field adjacent thereto, means for yieldably supporting said element for movement about a horizontal axis, means for yieldably setting said element to an initial position, said element setting means including a gear train, an electro-responsive device comprising a pair of voltage generators constructed and arranged to be activated selectively by said element in accordance with the direction of movement thereof from said initial position, means including a motor adapted to be operated in either direction selectively in accordance with the activated one of said voltage generators for driving said gear train thereby to automatically adjust said setting means to compensate for a variation in the gravitational pull on said element corresponding to a predetermined rate of change in either direction in the strength of said gravitational field. 7

References Cited in the file of this patent UNITED STATES PATENTS 1,310,568 Heap et al. July 22, 1919 1,382,374 Maxim June 21, 1921 1,491,004 Dufiie Apr. 22, 1924 1,538,316 Duffie May 19, 1925 1,579,273 Wright Apr. 6, 1926 2,183,115 Boucher Dec. 12, 1939 2,218,140 Wright et al. Oct. 15, 1940 2,367,126 James Jan. '9, 1945 

